THE CASCO BAY “MUD

SUMMIT”

Local efforts to look at acidification, clams and

nutrients

Curtis C. Bohlen

Director, Casco Bay Estuary Partnership

Casco Bay Estuary Partnership

One of 28 National Estuary Programs

We build consensus, facilitate communications and attract funds for protection of the Bay

Many partners

Focused, collaborative

Credible data and information

Strategic direction

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FOCB / CBEP 2012 Work on

Acidification

FOCB

Identified issue– ‘Death by Dissolution’

Initiated informal studies in 2011

Working with local scientists

Staff and interns collected preliminary data on pH of tidal flats

Led efforts to collect data in 2012

CBEP

Consulted on study design

Provided partial funding for additional data – sediment chemistry

Funded related clam abundance surveys

Hosted “Mud Summit”

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Casco Bay

About 200 Square Miles of Water

More than 575 miles of shoreline

785 islands, islets and ledges

A marine dominated coastal embayment

Tidal water exchange is (usually) much greater than river flow

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Casco Bay Marine Resources 5

Maine Fisheries by Value 6

Source: Maine DMR 2013

Maine Shellfish Co-management

Towns

Intertidal harvests only – Softshell clams

Shellfish Committees

Set number of licenses

Determine conservation measures

Harvesters required to contribute “conservation time”

Seeding of flats

Stock assessment

State (DMR)

Professional biologists, make recommendations to Committees

Health closures

Subtidal harvests (quahogs)

About 275 (Commercial) licenses in Casco Bay

Average cost ~ $241

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Softshell Clams at Lanes Island

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0

Nu

mb

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Millimeters

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2010 2012

Source: Marc-Nault, pers. com. 2013

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Possible Factors

Poor Recruitment

Predation

Over Harvest

Disease

“Bad Mud” (Ocean

Acidification?)

All of the above

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Carbon Dioxide And Water

More CO2 in the atmosphere leads to more CO2 in the oceans

When CO2 dissolves in water, the water gets more acidic

Changes in ocean chemistry

Carbonate saturation state, or “CSS”

Challenges for marine organisms with shells

Global CO2

Local sources of CO2

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Sediments in Casco Bay

Casco Bay Sediments

offer a harsher

microenvironment for

calcifying organisms

than does the

overlying water

At one Casco Bay tidal

flat, median sediment

CSS is around 0.75.

Green et al. 2009

Green et al. 2012

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Negative Impacts of CO2 on

Mollusks In the Lab

Tiny (0.2mm) Hardshell Clams (Mercenaria

mercenaria) grown in the lab at low CSS for 0,4,

And 7 days.

Green et al. 2009

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Behavioral Impacts

Green et al. 2012 Settlement of Mercenaria mercenaria in the lab

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2012 Field Sample Sites

Thirty (30) sites selected by contacting local informants in each town

Identify “Productive” and “Unproductive” flats

i.e., sites that are no longer considered productive

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Casco Bay Clam Flat Monitoring

Parameters 2012

Water pH and Temperature

Sediment pH

Sediment ORP

Sediment % Carbon

Sediment % Nitrogen

Sediment Surface Area

Clam population assessments

Limited data on Carbonate Saturation State (CSS)

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Distribution of Sediment pH

Parameter Value

Maximum 8.75

Median 7.54

Minimum 6.48

Mean 7.589

Standard Deviation 0.407

N 300 6.5

7

7.5

8

8.5

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Sediment pH

Distributions

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Sediment pH, Carbon and Nitrogen

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7.2

7.4

7.6

7.8

8

8.2

8.4

sed p

H

0 1 2 3 4 5 6 7

sed%C

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7.2

7.4

7.6

7.8

8

8.2

8.4

sed p

H0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

sed%N

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pH and Informant Assessment of

Productivity

“Productive” flats have

higher average pH

than “Unproductive”

Flats

Difference =

0.23 +/- 0.101

(p<0.05)

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pH and Shellfish Abundance

7.2 7.4 7.6 7.8 8.0 8.2

02

04

06

08

0

pH, Adult Clams, and

Informant Assessment of Productivity

pH

Ad

ults

Not Productive

Productive

7.2 7.4 7.6 7.8 8.0 8.2

05

10

15

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pH, Clam Spat, and

Informant Assessment of Productivity

pH

Sp

at

Not Productive

Productive

ADULTS SPAT

2012 Results

Accurate and repeatable sediment pH measurements

Some clam flats have very low sediment pH values

Clam flats qualitatively categorized as “productive” had higher mean pH values than “not productive” flats

But that pattern disappeared when compared to OBSERVED clam abundance

Sediment with low pH values has relatively high %C and %N

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Mud Summit

Originally imagined as

a small working

meeting

Invited CBEP STAC

Word got around,

ended up with more

than 30 people

Review science

Present results of

2012 field studies

Seek advice on next

steps

Articulate local

research priorities

Assist FOCB in

planning 2013 field

studies

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“Mud Summit” Results

Need to distinguish between two groups of questions:

Mechanisms of acidification

Effects on shellfish

Specific research suggestions

Need to understand spatial and temporal variability of both pH /CSS and shellfish

Need to document relationship between pH – easy and inexpensive to measure – and carbonate saturation

Recommendations for FOCB study 2013

Sample fewer sites, focus on spatial patterns

Transects across intertidal zone

Sample repeatedly

Collect more explanatory information

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